Apparatus, system, and method for electrostatic discharge protection

ABSTRACT

An apparatus, system, and method provide electrostatic discharge (ESD) protection in electronic devices by guiding electrostatic charges to a ground through ESD channels within electrical insulation sheet. The ESD channels are positioned within the electrical insulation sheet to provide electrical paths to ground having a lower impedance than electrical paths to protected areas covered by the electrical insulation sheet. Accordingly, an ESD follows the path of least resistance safely to ground rather than to a critical component within the electronic device. In the exemplary embodiment, the ESD channels are openings in a dome contact layer of a keypad where the openings are positioned over one or more ground areas of a printed circuit board (PCB) and the insulting material of the dome contact layer covers areas of the PCB that are protected from ESD. By implementing dedicated GPIO lines, grounded metal domes cover the signal pads in the target discharge area to protected the GPIO lines from ESD. Device components are protected from ESD without additional ports or insulation.

BACKGROUND OF THE INVENTION

The invention relates in general to electronic devices and morespecifically to an apparatus, system, and method for electrostaticdischarge (ESD) protection in an electronic device.

Electronic devices such as, for example, cellular telephones, personaldigital assistants (PDA), portable media players, and portable computersare susceptible to damage by electrostatic discharge (ESD). ESD is therapid and spontaneous transfer of electrical charge between two objects.One example of ESD that can be experienced particularly in dry climatesincludes the “shock” or spark resulting from the discharge ofelectrostatic charge when a hand or figure is placed near a doorknobafter the electrostatic charge has formed due to shuffling acrosscarpet. ESD occurs in a variety of situations, however, and does notneed to be felt to cause extensive damage to sensitive components inelectronic devices. Keypads, buttons, and other user interfaces onelectronic devices provide an especially vulnerable entry point forelectrostatic charges to reach electronic device components.

Some conventional designs reduce the susceptibility of electronicdevices to ESD by increasing the thickness of insulating materials atthe vulnerable areas. For example, the thickness of the shaped rubberlayer forming the keypad of a device can be increased to insulate thesensitive components from ESD. This technique is limited in that, due tothe increased thickness, the size of the overall size of the electronicdevice is increased. Further, the electronic device may be moredifficult and costly to manufacture since the thicker keypad requiresmore material and is more difficult to manipulate. Also, the thickermaterial may result in a keypad that is bulkier, less sensitive, andmore difficult to use.

Other conventional techniques for reducing susceptibility to ESD includethe placement of circuit elements such as diodes to “short out” ESD anddirect charges to ground. These methods, however, are limited in thatthe complexity and cost of the electronic device is increased.

Other conventional designs include a conductive escutcheon thatsurrounds at least some of the buttons of a keypad and is connected tothe ground of the electronic device. This technique is limited in thatthe escutcheon is difficult and costly to manufacture. Further, theescutcheon often can not be shaped to adequately protect the areas thatare vulnerable to ESD penetration. For example, as the sizes of the keysof keypads decrease, the available space for positioning the sections ofthe conductive escutcheon also decreases resulting in device areas thatare not adequately protected against ESD.

Accordingly, there is a need for an apparatus, system, and method forelectrostatic discharge (ESD) protection in an electronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a side view of an electronic device inaccordance with an exemplary embodiment of the invention.

FIG. 2 is a block diagram of a top view of the electrical insulationsheet over the printed circuit board of the electronic device.

FIG. 3 is an illustration of a perspective exploded view of the ESDprotection assembly in accordance with the exemplary embodiment wherethe electrical insulation sheet comprises a dome contact sheet.

FIG. 4 is an illustration of a top view of a portion of the PCB inaccordance with the exemplary embodiment.

FIG. 5 is an illustration of an exploded view of an electronic device inaccordance with the exemplary embodiment of the invention where theelectronic device is a cellular telephone.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An apparatus, system, and method provide electrostatic discharge (ESD)protection in electronic devices by guiding electrostatic charges to aground through ESD channels within electrical insulation sheet. The ESDchannels are positioned within the electrical insulation sheet toprovide electrical paths to ground having a lower impedance thanelectrical paths to protected areas covered by the electrical insulationsheet. Accordingly, an ESD follows the path of least resistance safelyto ground rather than to a critical component within the electronicdevice. In the exemplary embodiment, the ESD channels are openings in adome contact layer of a keypad where the openings are positioned overone or more ground sections of a printed circuit board (PCB) and theinsulting material of the dome contact layer covers areas of the PCBthat are protected from ESD.

FIG. 1 is a block diagram of side view and FIG. 2 is a top view of anESD protection assembly 100 of an electronic device in accordance withthe exemplary embodiment of the invention. The blocks in FIG. 1 and FIG.2 generally represent exemplary relative configurations of a printedcircuit board 102 and an electrical insulation sheet 104 for protectingareas 114 within the electronic device from electrostatic discharge(ESD) 106 and do not necessarily represent all relative sizes orpositions of the components illustrated. In the exemplary embodiments,the electrical insulation sheet 104 is implemented as part of a portablecommunication device such as, for example, a cellular telephone orwireless PDA.

As discussed above, electronic devices are susceptible to damage fromESD. An ESD source 108 such as a human figure or hand, metallic buttonon the device, or other object that may accumulate static charge,creates an electrostatic discharge (ESD) 106 when the impedance alongany path from the ESD source 108 to the electronic device issufficiently low. If the ESD path passes through or terminates at acritical component, damage can result. In the exemplary embodiment, theESD 106 are guided through discharge paths that avoid electricalcomponents and signal traces within discharge avoidance areas 114.

A discharge channel 110 within an electrical insulation sheet 104provides a relatively low impedance path to the ground potential of theelectronic device. The discharge channel 110 has a channel impedancethat is less than the insulation sheet impedance of the electricalinsulation sheet 104. The discharge channel 110 is positioned adjacentto an exposed ground area 112 of the printed circuit board 102.Accordingly, at least a portion of the ground area 112 is exposed underthe discharge channel 110 to provide a closed electrical path to thedevice ground for the ESD 106. The ground area 112 is a section ofcopper on the surface of the PCB 102 in the exemplary embodiment. Theground area 112 may include vias to other ground layers within the PCB102 and may have any of numerous shapes and sizes.

In the exemplary embodiment, the electrical insulation sheet 104comprises a plurality of discharge channels 110 which are formed byopenings in the electrical insulation sheet 104. The discharge channel110, however, may be formed using other techniques or components. Forexample, the discharge channel 110 may include a layer of insulationmaterial that is thinner than the insulation sheet 104 in somesituations. Also, a conductive material may be inserted or otherwisepositioned through the electrical insulation sheet 104 to provide theelectrical path to the exposed ground area 112. The discharge channel110, therefore, is any configuration, mechanism, or material that formsa path having a lower electrical impedance than the insulation sheet 104in order to guide the ESD 106 to a target discharge area within theelectronic device to avoid the discharge avoidance areas 114.

FIG. 3 is an illustration of a perspective exploded view of the ESDprotection assembly 100 in accordance with the exemplary embodimentwhere the electrical insulation sheet 104 comprises a dome contact sheet302. The dome contact sheet 302 includes a plurality of dome contacts304 that align with a set of contact pads 306-308 on the circuit board102 when the ESD protection assembly 100 is assembled. The dome contacts304 and contact pads 306-308 on the printed circuit board 102 form domecontact switches for buttons accessible from the exterior of theelectronic device. Each dome contact 304 is aligned with the set ofcontact pads 306, 308, that include a center connect pad 310 and aperipheral contact pad 312. As discussed in further detail withreference to FIG. 4, the peripheral contact pad 312 is part of theground area 112 for contact pads 306 within a target discharge area 314.

In the exemplary embodiment, the discharge channel 110 comprises aplurality of openings extending through the dome contact sheet 302. Theopenings are strategically aligned with target discharge locations 316on the PCB 102 within the target discharge area 314. Damage to theelectronic device due to ESD 106 is minimized by selecting targetdischarge locations 316 on the exposed ground area 112 of the PCB 102 ata safe distance from components and traces susceptible to ESD 106.Accordingly, an electrostatic discharge 106 to a target dischargelocation 316 results in a discharge that avoids the discharge avoidancearea 114.

FIG. 4 is an illustration of a top view of the PCB 102 in accordancewith the exemplary embodiment. In accordance with known techniques,electrical connections are formed between a pair of contact pads 306,308 when a dome contact 304 is depressed. As the dome contact 304 isdepressed, it deforms to contact a center contact pad 310 while aportion of the electrically conductive dome contact 304 is in contactwith a peripheral contact pad 312. An electrical connection between thecenter contact pad 310 and the peripheral contact pad 312 results. Oneor more of the contact pads 310, 312 are connected to a signal line. Inmany situations, a matrix formed with multiple signal lines includingdrive lines and sense lines allows a processor to determine activatedswitches based on unique combination connections between signals. Such aconfiguration minimizes the number of General Purpose Input Output(GPIO) lines that are dedicated to the keypad. The contact pads 306within the target discharge area 314, however, include a peripheralcontact 312 that is part of the ground area 112. In order to minimizethe possibility of an ESD 106 through the dome contact 304 to a signalline, the peripheral contacts 312 are grounded while the center contact310 is protected by the dome contact 304, which is in contact with theperipheral contacts 312, from ESD 106. Since one of the contact pads 312is connected to ground, dedicated GPIO lines are required to sense theactivation of the buttons corresponding to the dome contact switches.Since many GPIO lines remain unused in electronic devices, such arequirement is typically not an issue in most designs.

FIG. 5 is an illustration of an exploded view of an electronic device500 in accordance with the exemplary embodiment of the invention wherethe electronic device is a portable communication device such as acellular telephone. Any of numerous configurations and components can beused to form any of several types of devices that include the ESDprotection methods and apparatuses in accordance with the descriptionsherein. A flexible keypad 502 extends through a front portion of ahousing 504 to provide a mechanism for activating the dome contactswitches. A chrome key pad 506 accessible through an opening on thefront portion of the housing 504 includes buttons for activating domecontact switches near a speaker 508. In the exemplary embodiment, thespeaker 508 is positioned behind the chrome key pad 506 within a plasticspeaker housing 510. The speaker housing 510 is positioned within arecessed area in the flexible keypad 502. Other components such asvisual displays 512 also extend through openings within the housing 504.

In the exemplary embodiment, the chrome key pad 506 is a floatingmetallic object that accumulates chargers. The resulting increase inelectrical potential will eventually find an electrical path todischarge. To avoid damage to components with the electronic device 500,at least one device discharge path 514 to the device ground is createdby strategically positioning the discharge channels 112 in the domecontact sheet 302. A discharge path, therefore, includes one of thedischarge channels 112 through the electrical insulation sheet 104 (domecontact sheet 302). The discharge path 514 provides a low impedance pathto the ground area 112 that is lower than other paths from the exteriorof the device 500. Accordingly, any ESD 106 is routed through theelectronic device 500 without passing through the discharge avoidancearea 114 thereby minimizing the likelihood of damage to the devicecomponents.

Therefore, in the exemplary embodiment, an electronic device 500 such asportable communication device includes a discharge path 514 for guidingESD 106 to a ground area 112 of a printed circuit board 102. One or moredischarge channels 110 within the electrical insulation sheet 104 havechannel impedances less than the insulation electrical impedance of theelectrical insulation sheet providing a relatively low impedance pathfor the ESD 106 to ground. The electrical insulation sheet 104 comprisesa dome contact sheet 302 in the exemplary embodiment where a targetdischarge area 316 is formed over the exposed ground area 112.Accordingly, susceptibility to ESD 106 is minimized without additionalcomponents or insulation.

Clearly, other embodiments and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. The above description is illustrative and not restrictive.This invention is to be limited only by the following claims, whichinclude all such embodiments and modifications when viewed inconjunction with the above specification and accompanying drawings. Thescope of the invention should, therefore, be determined not withreference to the above description, but instead should be determinedwith reference to the appended claims along with their full scope ofequivalents.

1. An electrostatic discharge (ESD) protection device comprising: anelectrical insulation sheet having an insulation electrical impedanceand having a discharge channel having an channel electrical impedanceless than the insulation electrical impedance and configured to directan electrostatic discharge to a ground potential of the portable device.2. An ESD protection device in accordance with claim 1, wherein thedischarge channel is an opening within the electrical insulation sheetpositioned adjacent to a ground area of a printed circuit board.
 3. AnESD protection device in accordance with claim 2, wherein the electricalinsulation sheet is a dome contact sheet comprising a plurality of domecontacts configured to make electrical connections on the printedcircuit board when deformed.
 4. An ESD protection device in accordancewith claim 1, wherein the electrical insulation sheet has a plurality ofdischarge channels having channel impedances less than the insulationelectrical impedance.
 5. An electronic portable device comprising: aprinted circuit board comprising a ground area; an electrical insulationsheet having an insulation electrical impedance and having a dischargechannel having an channel electrical impedance less than the insulationelectrical impedance, the electrical insulation sheet positionedadjacent to the printed circuit board to align the discharge channelover at least a portion of the ground area.
 6. An electronic portabledevice in accordance with claim 5, wherein the discharge channel isconfigured to direct an electrostatic discharge originating on a sideopposite the printed circuit board to the ground area.
 7. An electronicportable device in accordance with claim 5, wherein the electricalinsulation sheet comprises a plurality of dome contacts positionedadjacent to a plurality of contact pads on the printed circuit board,each dome contact configured to form an electrical connection between acenter contact pad and a peripheral contact pad when deformed.
 8. Anelectronic portable device in accordance with claim 7, whereinperipheral contact pad comprises a ground potential contact area.
 9. Anelectronic portable device in accordance with claim 8, furthercomprising: a housing at least partially enclosing the printed circuitboard and the electrical insulation sheet; and device circuitry withindischarge avoidance areas, the portable electronic device having atleast one device discharge path extending from an exterior of thehousing through the discharge channel to the ground area and having apath impedance less than any undesired discharge path passing throughthe device circuitry.
 10. An electronic portable device in accordancewith claim 9, wherein the device circuitry comprises signal traces onthe printed circuit board.
 11. An electronic portable device inaccordance with claim 9, wherein the device circuitry compriseselectrical components on the printed circuit board.
 12. An electronicportable device in accordance with claim 9, wherein the device circuitrycomprises wires extending from the printed circuit board.
 13. A portablecommunication device comprising: a printed circuit board comprising aground area and a plurality of contact pad sets comprising a centercontact area and a peripheral contact area; an electrical insulationsheet comprising a plurality of dome contacts poisoned over the contactarea pairs and configured to form an electrical connection between acorresponding center contact area and a corresponding peripheral contactarea, the electrical insulation sheet having a plurality of dischargechannels having electrical impedances less than a sheet electricalimpedance of the electrical insulation sheet and positioned adjacent toat least portions of the ground area.
 14. A portable communicationdevice in accordance with claim 13, wherein the discharge channels areconfigured to direct an electrostatic discharge originating on a sideopposite the printed circuit board to the ground area.
 15. A portablecommunication device in accordance with claim 13, wherein the peripheralcontact pad comprises a ground potential contact area.
 16. A portablecommunication device in accordance with claim 13, further comprising: ahousing at least partially enclosing the printed circuit board and theelectrical insulation sheet; and device circuitry within dischargeavoidance areas, the portable communication device having at least onedevice discharge path extending from an exterior of the housing throughthe discharge channel to the ground area and having a path impedanceless than any undesired discharge path passing through the devicecircuitry.
 17. A portable communication device in accordance with claim16, wherein the device circuitry comprises signal traces on the printedcircuit board.
 18. A portable communication device in accordance withclaim 16, wherein the device circuitry comprises electrical componentson the printed circuit board.
 19. A portable communication device inaccordance with claim 16, wherein the device circuitry comprises wiresextending from the printed circuit board.
 20. A portable communicationdevice in accordance with claim 16, further comprising an electricallyconductive button, device discharge path passing through electricallyconductive button.